Which effect describes when a language learner's progress plateaus despite extensive study?

The concept of fossilization is crucial to understanding why a language learner's progress can plateau despite continued study. Fossilization refers to the process where specific forms or aspects of a learner's language become fixed and resistant to further change. This can occur when learners consistently use incorrect structures or vocabulary that they have acquired over time, leading to persistent errors that remain despite more advanced study or practice.

In this scenario, even though the learner is engaged in extensive study, they may not be incorporating corrections or developing their skills further because their established patterns have become 'fossilized.' This phenomenon illustrates a common challenge in language acquisition where learners may reach a certain level of proficiency but struggle to advance beyond that point due to ingrained habits and language use that do not evolve.